Particle ejection during mergers of dark matter halos

TL;DR

This paper investigates how dark matter particles are ejected during halo mergers, showing that rapid potential changes cause ejection and that a significant fraction of particles from the smaller halo are expelled.

Contribution

It demonstrates that rapid mean field potential changes, not dynamical friction, cause particle ejection during dark matter halo mergers, with detailed simulation analysis.

Findings

5-15% of small halo particles are ejected during mergers

Ejected particles mainly originate from the small halo

Rapid potential changes drive particle ejection, not dynamical friction

Abstract

Dark matter halos are built from accretion and merging. During merging some of the dark matter particles may be ejected with velocities higher than the escape velocity. We use both N-body simulations and single-particle smooth-field simulations to demonstrate that rapid changes to the mean field potential are responsible for such ejection, and in particular that dynamical friction plays no significant role in it. Studying a range of minor mergers, we find that typically between 5-15% of the particles from the smaller of the two merging structures are ejected. We also find that the ejected particles originate essentially from the small halo, and more specifically are particles in the small halo which pass later through the region in which the merging occurs.